Conventionally, as a support for active substances such as various catalysts, etc., there are proposed formed articles in the form of a membrane or microcapsules that is or are hollow or structurally porous.
For example, there has been proposed a membrane having a continuous porous structure having a spinodal separation pattern (see Patent Document 1). Further, porous spherical particles are known for a support for various catalysts, electrophotographic toners, an electronic material for displays, chromatography, adsorbents, etc. (see Patent Document 2). As an immobilizing carrier for active matters typified by microorganisms, bacteria and enzymes, further, there has been proposed a microcapsule having a hollow space and a porous capsule wall and having a structure in which cells of the capsule wall communicate with the hollow space in the capsule through fine pores (see Patent Document 3). Further, there has been proposed a microcapsule having intended sustained releasability based on the control of denseness of a capsule resin wall material (see Patent Document 4). As a method for imparting a binder for an active substance with a porous structure, further, there has been proposed a method that uses, as a cells-forming agent, an inorganic salt or an organic material such as starch (see Patent Document 5).
A microcapsule is a fine container formed by covering an inclusion in the form of a solid, liquid or gas with a thin film wall material, and it has functions of protecting an unstable substance, isolating a reactive substance, controlling the diffusion of the inclusion or including an active substance or matter. For causing a microcapsule to exhibit these functions effectively, it is required to ensure that a substance outside the capsule can efficiently contact an included active substance by easy molecular diffusion without causing a pressure loss.
However, conventional microcapsules are formed each of a hollow portion and a shell covering it, the interior of each capsule is hollow, and the space and internal surface area for holding an active substance inside are limited.
Further, in microcapsules having a large particle diameter each, it is required to increase the thickness of a shell for maintaining the strength thereof. However, an active substance and a substance outside the capsule contact each other only through pores that exist in the shell and have a size of several nm to tens nm, and there is a defect that when the thickness of the shell is increased, the pressure loss by these pores increases and no efficient contact can be attained.
Further, since active substances are generally fine particles, there is involved a problem that when they are used in a packed column, impractically, the pressure loss is large. For overcoming this problem, it is general practice to fix an active substance with a binder to be granulated, and form particles. In this method, however, the active substance surface is coated with the binder, and no surface area effective for exhibition of a function can be secured. There has been hence proposed a method in which a binder is caused to include, as a cells-forming agent, an inorganic salt or an organic substance such as starch and the cells-forming agent is removed by washing, etc., after the formation of capsules. However, the defect is that no holes communicating with an outside are obtained and that the production cost thereof is also increased.
Further, when an active substance has a coagulation structure, there is a problem that part of the active substance easily comes off or separates due to an external friction or the like in a portion where the active substance is exposed directly to an external atmosphere.
Further, concerning an active substance having physiologically high activity, it is required to prevent its direct contact to a human body or its suction into a human body. In this case, it is required to coat the active substance surface with a thin film of a polymer or the like, and the problem with this is that when the coating polymer has no communicating holes, the active substance does not effectively work.
(Patent Document 1) JP 1-245035A
(Patent Document 2) JP 2002-80629A
(Patent Document 3) JP 2003-88747A
(Patent Document 4) JP 2004-25099A
(Patent Document 5) JP 64-65143A